This invention relates to a reverse profiling method for profiling a modulated impurity density distribution of a semiconductor device.
An impurity density distribution of a semiconductor device is an important factor, which affects electric characteristics of the semiconductor device. Accordingly, measurement of the impurity density of the semiconductor device is very important to analyze or inspect the semiconductor device. In other words, it is very important to extract the impurity density distribution profile of the semiconductor device for analysis or inspection of the semiconductor device.
However, it is very difficult to directly measure the impurity density of the semiconductor device. Therefore, a reverse profiling method is used for profiling the impurity density distribution.
A conventional reverse profiling method measures actual electric characteristics of the semiconductor device while it performs simulation to find simulative electric characteristics of the semiconductor device. Initial parameters used in the simulation are decided on the basis of producing condition of the semiconductor device. The simulation is repeated until the simulative electric characteristics practically match the measured actual electric characteristics. Parameters used in the simulation are changed whenever the simulation is repeated. When the simulative electric characteristics practically match the measured actual electric characteristics, the parameters used in the simulation are substituted in a predetermined analytical equation to find the impurity density distribution.
Such a reverse profiling method is proposed by Z. K. Lee et al. in their article of "Inverse Modeling of MOSFETs USING I-V Characteristics in the Subthreshold Region", IEDM Tech. Dig., pp683-685, 1997.
By the way, in a production of an MOSFET, source/drain impurities are implanted into a substrate, which is annealed after to activate the source/drain impurities. The annealing process acceleratingly diffuses the channel impurities located beside the source/drain regions. That is, the annealing modulates distribution of the channel impurities. The conventional reverse profiling method can find an approximate profile of the modulated distribution of the channel impurities together with an approximate profile of the source/drain impurity density distribution.
However, the conventional reverse profiling method can not quantitatively find modulation effect of the annealing process to the channel impurity density distribution. This is because the conventional reverse profiling method uses the measured electric characteristics of only one type of the MOSFETs.
Moreover, the conventional reverse profiling method needs a long time to match the simulative electric characteristics with the measured actual electric characteristics. This is because the conventional reverse profiling method repeats the simulation with change of the parameters.
Still moreover, the found profile by the conventional reverse profiling method is not always unique. This is because the parameters are changed at a time to extract plural profiles at the same time in the conventional reverse profiling method.